Incandescent lamp



1965 E. a. AUDESSE ETAL 3,225,247

INCANDESCENT LAMP Filed June 13, 1962 FIG.|

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E S EG m SDMT S R E E D LV $AN A P G Y S REE ww ERM ATTORNEY United States Patent Ofifice 3,225,247 Patented Dec. 21, 1965 3,225,247 HNCANDESCENT LAMP Emery G. Audesse, Salem, Mass., James J. Palermo, Salem, N.H., and Robert F. coledge, Danvers, Mass., assignors to Sylvania Electric Products Inc, a corporation of Delaware Filed June 13, 1962, Ser. No. 202,309 9 mantis. (Cl. 313-271) This invention relates to incandescent lamps, and particularly to those in which a coiled-coil filament ext-ends longitudinally through a tubular light-transmitting envelope. However, it can be used more generally, where coiled-coil filaments require support at various positions along their length.

In some lamps, the coiled-coil filament is short enough with respect to its length, and of heavy enough wire, so as to be self-supporting when held at its ends. In other cases the filament requires support at one or more positions along its length, and this is especially true with the longer filaments of small diameter wire used at high voltages, such as 230 volts, for example. When the filament is enclosed in a tubular envelope of small diameter, a small sag in the filament may cause it to touch the glass tube, and the danger of blistering the glass is a serious difiiculty.

However, even if the sag were not enough to bring the filament against the tube, it could be sufiicient to permit vibration of the filament, especially when the lamp is used in motion picture projection apparatus operated by a motor, and to damage the filament when subjected to shock in transportation or the like, and especially when subjected to any shock while hot. Supporting the coil at one or more positions along its length will overcome such difficulties.

In the usual globular glass bulbs customarily used in lamps of the types designed for general illumination, there is a glass stem or a glass button into which wires can be sealed to support the middle portions of the coil. In the elongated tube type of lamp, however, the filament must be sup-ported from its ends and from supports fitting against the inner circumference of the tube, since support wires cannot be sealed into the tube along its length, be cause the tube wall is thin.

When the filament is singly-coiled, that is, coiled only once, the coil can be spaced from the inner wall of the tube by discs or wire spirals of molybdenum, tungsten or tantalum. However, when the coil is a coiled-coil of closely spaced turns, the supporting disc or spiral would not fit transversely between turns, because of their pitch, but would tend to be at an angle with the coil, and would in any event short-circuit a turn of the larger or secondary coiling. When the coil is a single coil, shorting one turn is not important, since the one turn is a small percentage of the total number. But when the coil is a coiled-coil, a shorted turn in the secondary coiling means a large number of shorted turns in the primary coil, and hence a larger percentage of the total. And so of course, the exact number of turns shorted might vary from time to time and from lamp to lamp.

We have discovered, however, that if a coiled-coil is cut at some point along its length, and the two adjacent cut ends joined by a larger tungsten wire formed into a loop which makes a sliding fit with the inside of the glass tube, the necessary support and spacing for the coil can be achieved without the disadvantages mentioned above. The whole filament, including spacers, can be slipped into the glass tube as an integral unit. The ends of the tungsten wire in the loop can be of a size such as to make a tight fit when slipped into the primary coil as if the coil were wound around it, and the loop between the ends of the tungsten wire can have the same pitch as the secondary winding of the coiled-coil itself.

The tungsten spacer wire has a diameter about equal to the inside diameter of the smaller or primary winding of the coil, so that it can be slipped inside the coil and hot-crimped to the wire of the coil.

We have also discovered that if the coil ends are not merely cut, but are formed to have straight singly-coiled legs extending transversely toward the wall of the tube, and the tungsten wire loop is made to be less than a complete turn, with straight ends extending inwardly in an approximately radial manner, the straight ends of the wire can be fitted into the singly-coiled legs at the ends of the coil. The ends of the loop, if made long enough, would cross each other and short circuit if the loop were in a single plane, but making it with a small pitch, such as that in the secondary coil itself, insures that the ends will be spaced apart, and not touching where they cross each other, that is where the projection into a single plane would cross.

Such a space can be placed at the middle of the coil in some cases, but in general the middle of the coil is the most efiective portion optically and may be coordinated with a reflector or lens, and a break at such a point would be undesirable, causing loss of light output. Moreover, the coolest part of the filament would be at its optical center, because the ends connected by the wire loop would operate cooler than other portions of the coil, due to the heat capacity of the loop and the conduction of heat by the loop from the filament to the glass.

In order to keep the middle portion of the filament continuous, we have discovered that it is generally desirable to use two spacers, even where only one would be needed for mechanical support, the spacers being nearer to the outside ends of the overall coil and supporting a considerable length of filament between them. We have found that a particularly useful arrangement is to make two identical coils, each having its ends extending transversely to the longitudinal axis of the coil as legs, and cut one coil at its middle. One complete coil with legs is used as the middle coil, and each half of the cut coil connected to an end of the middle coil by the tungsten loops previously described. The leg of the end coil is placed adjacent a leg of the middle coil, so a leg of a coil can he slipped over each straight end of the wire loop, and the legless end of the coil connected to a lead-in and support wire in the manner shown in a copending application of Scoledge, Bonazoli and Palermo filed on or about May 31, 1962.

Where the lamp contains iodine vapor, often used to reduce discoloration of the envelope, the supporting and spacing loop is made of tungsten, because molybdenum, nickel and the like would not be kept from depositing on the wall by the iodine. However, in lamps where the iodine is not present, nickel or molybdenum loops can be used.

We have discovered that with lamps as described above, the end coils sometimes burn out first at the end of life, while the middle coil is still intact and suitable for further life. We have further discovered that burnout of the end coils can be prevented and the lamp made useful for the entire life of the middle coil, by making the end coils of slightly larger-diameter wire than the middle coil, while keeping the inside diameter of the primary coil the same as that of the middle coil, so that the ends of the spacing or joining loop can be fitted properly into each coil. In this way the end coils will have longer life than the middle coil, without any serious reduction in the total useful light output, because the ends of the coil are less than effective than the middle with most optical equipment, such as reflectors.

Other objects, advantages and features of the invention will be apparent from the following specification taken with the accompanying drawing, in which:

SIG. 1 is a view of a lamp according to the invention; an

FIG. 2 is a cross-sectional view of the lamp, showing the tungsten wire spacing loop in more detail.

In FIG. 1, the tubular lamp envelope 1 is of quartz or other refractory glass such as one of almost pure silica, such as that sold under the trademark Vycor by the Corning Glass Works, Corning, New York. The tubular portion has a length of about one and one-half inches in an 800-watt lamp, which is the one here described. The tubular portion 2. has an outside diameter of about one-half inch, and a wall thickness of about 0.05 inch, making the inside diameter about 0.4 inch. The flattened end portions 3 of the envelope have the ridges 4, 4 at their sides in the usual manner, as shown, for example, in a copending application, filed on or about May 31, 1962, by Scoledge, Bonazoli and Palermo. The end caps S, 5, as in the latter application, are of insulating material, each having a central contact connected to a wire (not shown) extending therefrom to a molybdenum ribbon 6, sealed through a flattened end 3 of the quartz envelope 1. A tungsten lead-in wire 7 extends into the tubular portion 2 of envelope 1 from the molybdenum ribbon 6 to fit into the end 8 of the primary winding of the coiled-coil coil 9. With respect to wire 7, the end fitting into coil 9 is curved so that it will fit properly, as in the Scoledge application previously mentioned. The end of the coil can be hot-crimped to the tungsten wire 7 by being pressed between electrodes in a low-voltage resistance welder.

The outside coils 9, 9 and the inside coil 10 are connected by the tungsten wire loops 11, which not only connect the coils electrically, but also support them in a spaced manner from the tube walls 2 as shown in crosssection in FIG. 2. Each end of a loop fits into an end of coil 9 and an adjacent end of coil 10, the wire of the loop having a diameter such that it can be slipped into an end of the coils, and when slipped into it is hot-crimped to the coil wire near the end of the coil, as at 13, 14.

The wire loops 11 are curved to form almost a complete turn of a spiral, as shown in FIG. 2, the ends of the loops 11 being bent inwardly to be slipped into adja cent ends of the coils 9, 10. The pitch of the spiral can be about equal to that of the secondary winding of the main coil.

Coils 9, 9 and 10 are of tungsten wire 5.7 mils in diameter, the total length of wire in all three coils being about 1400 millimeters. The coils are first wound at 103 turns per inch on a mandrel having a diameter of 24.7 mils and then this primary coil with the mandrel in place is wound about a second mandrel of about 40 mils diameter to form a secondary winding of about 24 /2 turns per inch. The mandrels are then removed in the usual manner. The middle coil 10 has about 9 secondary turns and the end coils have about 4 /2 turns each, making a total of 18 turns in all. The portions 13, 14 which extend over the wire loops 11 are about 7 long. The straight portions of wire loops 11 are also about 7 long and the curve portion of the loop extends through an angle of about 300.

The middle coil can be made with the portions 13, 14 extending out from the coil as legs, so that they can readily fit over the ends of the wire loops. One such coil can be used as the middle coil 10, and an identical coil cut at its middle to form two end coils, leg of the end coil being placed adjacent a leg of the middle coil, and the cut end fitted over a lead-in wire 7.

The coils described above would be all of the same wire size and pitch. In such an arrangement, the end coils sometimes burn out first, leaving the middle coil still intact. Accordingly, it is desirable to make the end coils of slightly larger wire than the middle coil, so that they will not burn out first, but will allow the middle coil to burn to the end of its own life. Making the end coils of larger wire increases the life of the lamp by reducing the chances of a burnout in some part of the filament at a given period of life. In any group of lamps, the proportion which would have burned out in the end coils will no longer burn out as soon and the average life of a group of lamps will be increased.

The end coils 9 can be formed by winding a 5.8 inch diameter wire to 103 turns per inch, 271 turns in all, on a 24.75 mil molybdenum mandrel, forming a primary coil which is then wound on a 45.0 mil steel pin at about 24.5 turns per inch, 9% turns in all, with singly-coiled end legs 3 mm. long, and then cut at its mid-point as in the preceding example, to form two coils 9.

The middle coil can be wound of 5.65 inch wire at the same 103 turns per inch on a 24.75 mil mandrel to a length of 250 turns, and then this primary coil wound on a 40.0 mil steel pin at 24.5 turns per inch to a length of about 9.2 turns, with 3 mm. long singly-coiled legs.

Various modifications of the examples described can be made by a worker skilled in the art without departing from the spirit and scope of the invention.

For example, in the embodiment described about the ends of the loops-11 cross each other without touching. However, in some cases it may be desirable to have them touch and short circuit to reduce the resistance heating effect in them and to avoid overheating the glass where the loop bears against it.

What we claim is:

1. An incandescent lamp comprising a sealed tubular light-transmitting envelope, a coiled-coil filament having a primary and a secondary coil within said envelope, said coiled coil filament including at least two separate coils, and a wire of larger diameter than that of said filament, each end of said wire fitting into the adjacent end of the secondary coil of each coiled coil filament, the wire being formed between its ends to a loop fitting against the inner wall of said tubular envelope.

2. The lamp of claim 1, in which the wire loop is wound in helical form to slightly less than a single turn, with its ends bent inwardly and straight to engage the ends of said coil.

3. The lamp of claim 2, in which an end of each coil other than an end engaging the wire loop is connected to a lead-in support wire.

4. An incandescent lamp comprising a sealed lighttransmitting envelope, a coiled-coil filament having a primary and a secondary within said envelope, said coiledcoil filament having a middle coil and two end coils, an end of each end coil being adjacent an end of said middle coil, and a wire of larger diameter than said filament, one end of said wire fitting into an end of the primary coil of an end coil and the other end of said wire fitting into an adjacent end of the middle coil, said wire being wound between its ends into a loop fitting against the inner wall of said tubular envelope.

5. The lamp of claim 4, in which the wire loop is wound in helical form to less than a single turn but more than half a turn, with its ends bent inwardly and straight to engage the ends of said coil.

6. The lamp of claim 4, in which wires extend from each end of the tubular envelope to engage the corresponding and otherwise free ends of the end coils.

7. A coiled-coil filament unit for a tubular incandescent lamp, said coiled-coil having a primary and a secondary coil and comprising a middle coil and an end coil on each side of said middle coil, and a wire loop of larger diameter than said middle coil and end coils, the wire of said loop being of a diameter to fit closely inside the secondary turns of said coils, an end of each said wire loop fitting into the end of the secondary coil of an end coil and an adjacent end of the secondary coil of said middle coil.

8. A coiled-coil filament unit for a tubular incandescent lamp, said coiled-coil having a primary and a secondary coil and comprising a middle coil and an end coil on each side of said middle coil, and a wire loop of larger diameter than said middle coil and end coils, the Wire of said loop being of a diameter to fit closely inside the secondary turns of said coils, an end of each said wire loop fitting into the end of the secondary coil of an end coil and an adjacent end of the secondary coil of said middle coil, the end coils being of larger diameter Wire than the middle coil, and the primary coil of the middle coil having the same inside diameter as the primary coil of the end coil so that it will 'fit over the corresponding end of the wire of the loop.

9. A tubular incandescent lamp having a series of coiled-coil wire filament segments, the separate segments in the filament so that there will be alternate hot and cool portions of the series of filaments.

References Cited by the Examiner UNITED STATES PATENTS 923,797 6/1909 McNeill 313284 X 1,125,121 1/1915 Knight 313-284 1,247,068 11/1917 Benbow 313279 2,342,044 2/1944 Foote 313279 2,454,765 11/1948 Braunsdorlf 313344 2,997,617 8/1961 Hodge 313-344 JOHN W. HUCKERT, Primary Examiner.

being connected by a Wire of larger diameter than that 15 JAMES D. KALLAM, Examiner. 

1. AN INCANDESCENT LAMP COMPRISING A SEALED TUBULAR LIGHT-TRANSMITTING ENVELOPE, A COILED-COIL FILAMENT HAVING A PRIMARY AND A SECONDARY COIL WITHIN SAID ENVELOPE, SAID COILED COIL FILAMENT INCLUDING AT LEAST TWO SEPARATE COILS, AND A WIRE OF LARGER DIAMETER THAN THAT OF SAID FILAMENT, EACH END OF SAID WIRE FITTING INTO THE ADJACENT END OF THE SECONDARY COIL OF EACH COILED COIL FILAMENT, THE WIRE BEING FORMED BETWEEN ITS ENDS TO A LOOP FITTING AGAINST THE INNER WALL OF SAID TUBULAR ENVELOPE. 